The invention relates to a digital process for controlling the correct reproduction of a composite television signal recorded on an information-carrying medium and to a device using this process.
The invention applies more particularly to a transparent videodisk optical reader carrying information recorded on both its faces.
The present standards for a color television system of the SECAM type (line by line alternate chrominance system) define specific signals intended to identify the analysis lines of the image carrying a first so-called D'R chrominance signal and the one carrying a second so-called D'B chrominance signal. These signals are situated in a time interval of nine consecutive lines, included in the time for the frame scanning return. These are lines 7 to 15 of the first frame and lines 320 to 328 of the second frame. These identification signals are composed of chrominance subcarrier salvos of a duration equal to that of the line, except for the line suppression time.
This identification system, though it is perfectly suitable for public transmission in the SECAM system, is however not optimized for certain applications, and in particular in the case of a videodisk recording.
It is also customary, in the known art, to multiplex standardized synchronization pulsed signals with the video luminance signal. This multiplexing usually takes place on the amplitude during the frame and line return times. This method presents several disadvantages: on the one hand, all the available amplitude for modulating the video signal cannot be used, on the other hand, the synchronization taking place on the edge of these signals, any deterioration of these signals or any superimposition of parasite signals may cause synchronization faults.
Different processes and devices have been proposed:
(1) for freeing to a large extent the line and frame return intervals;
(2) for transcoding in a simple way television signals recorded according to a sequential type television system with any desired system, for example NTSC or PAL;
(3) for using the freed intervals for recording sound signals accompanying the television images in digital form.